Sub-pixel regions on the faceplate of a flat panel display are typically separated by an opaque mesh-like structure commonly referred to as a matrix or "black matrix". By separating sub-pixel regions, the black matrix prevents electrons directed at one sub-pixel from being overlapping another sub-pixel. In so doing, a conventional black matrix helps maintain color purity in a flat panel display. In addition, the black matrix is also used as a base on which to locate structures such as, for example, support walls. In addition, if the black matrix is three dimensional (i.e. it extends above the level of the light emitting phosphors), then the black matrix can prevent some of the electrons back scattered from the phosphors of one sub-pixel from impinging on another, thereby improving color purity.
Polyimide material may be used to form the matrix. It is known that polyimide material contains numerous components such as nitrogen, hydrogen, carbon, and oxygen. While contained within the polyimide material, these aforementioned constituents do not negatively affect the vacuum environment of the flat panel display. Unfortunately, conventional polyimide matrices and the constituents thereof do not always remain confined within the polyimide material. That is, under certain conditions, the polyimide constituents, and combinations thereof, are released from the polyimide material of the matrix. As a result, the vacuum environment of the flat panel display is compromised.
Polyimide (or other black matrix material) constituent contamination occurs in various ways. As an example, thermally treating or heating a conventional polyimide matrix can cause low molecular weight components (fragments, monomers or groups of monomers) of the polyimide material to migrate to the surface of the matrix. These low molecular weight components can then move out of the matrix and onto the faceplate. When energetic electrons strike the contaminant-coated faceplate, polymerization of the contaminants can occur. This polymerization, in turn, results in the formation of a dark coating on the faceplate. The dark coating reduces brightness of the display thereby degrading overall performance of the flat panel display.
In addition to thermally induced contamination, conventional polyimide matrices also suffer from electron stimulated desorption of contaminants. That is, during operation, a cathode portion of the flat panel display emits electrons which are directed towards sub-pixel regions on the faceplate. However, some of these emitted electrons will eventually strike the matrix. This electron bombardment of the conventional polyimide matrix results in electron-stimulated desorption of contaminants (i.e. constituents or decomposition products of the polyimide matrix). These emitted contaminants arising from the polyimide matrix are then deleteriously introduced into the vacuum environment of the flat panel display. The contaminants emitted into the vacuum environment degrade the vacuum, can induce sputtering, and may also coat the surface of the field emitters.
Furthermore, conventional polyimide matrices also suffer from X-ray stimulated desorption of contaminants. That is, during operation, X-rays (i.e. high energy photons) are generated by, for example, electrons striking the phosphors. Some of these generated X-rays will eventually strike the matrix. Such X-ray bombardment of the conventional polyimide matrix results in X-ray stimulated desorption of contaminants (i.e. constituents or decomposition products of the polyimide matrix). As described above, these emitted contaminants arising from the polyimide matrix are then deleteriously introduced into the vacuum environment of the flat panel display. Like electron stimulated contaminants, these constituents degrade the vacuum, can induce sputtering, and may also coat the surface of the field emitters.
The faceplate of a field emission cathode ray tube requires a conductive anode electrode to carry the current used to illuminate the display. A conductive black matrix structure also provides a uniform potential surface, reducing the likelihood of electrical arcing. Unfortunately, conventional polyimide matrices are not conductive. Therefore, local charging of the black matrix surface may occur and arcing may be induced between the cathode and a conventional matrix structure.
Thus, a need exists for a matrix structure which does not deleteriously outgas when subjected to thermal variations. Another need exists for a matrix structure which meets the above-listed need and which does not suffer from unwanted electronor photon-stimulated desorption of contaminants. Finally, still another need exists for a matrix structure which meets both of the above needs and which also achieves electrical robustness in the faceplate by providing a constant potential surface, which reduces the possibility of arcing.